The present invention relates to a process for the conversion of high boiling organic materials to lower boiling materials, and more particularly, to a method of recovering fuel range liquids from oil-containing compositions such as petroleum, coal, oil shale, shale oil, tar sand solids, bitumen and heavy hydrocarbon oil.
The potential reserves of liquid hydrocarbons which are contained in subterranean carbonaceous deposits have been identified as being substantial. Tar sands and oil shales represent two of the major potential resources of oil. In fact, the potential reserves of liquid hydrocarbons to be derived from tar sands and oil shales is believed to exceed the known reserves of liquid hydrocarbons to be derived from petroleum. However, the exploration of these potential reserves has been limited by the previously low priced and abundant supply of liquid crude oil and the process difficulties of extracting the heavier more viscous organic materials from tar sands and oil shales.
More recently, however, because of the ever increasing costs of liquid crude oils and the ever present threat of reduced availability from foreign sources, there is significant interest in improving the economics of recovering liquid hydrocarbons and in particular, fuel range liquids from tar sands and oil shale sources on a commercial scale. Methods have been suggested for recovering hydrocarbons from tar sands and oil shales, but the methods generally have not been accepted because of their high costs which renders recovered hydrocarbons too expensive to compete with petroleum crudes which can be recovered by more conventional methods.
The extraction of oil from tar sands and oil shales requires a physical separation process to break the oil/sand or shale bond. This can be achieved using hot water, steam and a diluent. Such a process requires high temperatures and very large amounts of energy are required to effect the process.
The crude oil produced from both tar sands and oil shales requires further processing to convert it to an acceptable refinery feedstock. The tar sands crude is a heavy extremely viscous high sulfur crude generally requiring that it be coked and hydrogenated or alternatively, hydrocracked. The oil recovered from shale retorts is similar to conventional crudes in some respects and is extremely viscous and contains a high nitrogen content.
The value of the hydrocarbons which have been recovered from oil shale and tar sands also has been diminished due to the presence of certain contaminants such as sulfur-, nitrogen, and metallic compounds which have a negative effect on the catalyst utilized in many of the processes to which the recovered hydrocarbons may be subjected. The contaminants also are undesirable because of their disagreeable odor, corrosive characteristics and combustion products.
Petroleum oil fractions produced by atmospheric or vacuum distillation of crude petroleum also are characterized by relatively high concentration of metals, sulfur and nitrogen. The high level of impurity results because substantially all of the contaminants present in the original crude remain in the residual fraction. The high metals content of the residual fractions generally preclude their effective use as charge stocks for subsequent catalytic processing because the metal contaminants deposit on the special catalyst for the processes and also result in the formation of inordinant amounts of coke, dry gas and hydrogen. For example, the delayed coking process has been effected on heavy residium fuels to obtain lower boiling cracked products. The process is considered a high severity thermal cracking process and yields large amounts of coke-by-product.
As mentioned above, many suggestions have been made in the prior art for recovering useful oil fractions from tar sands and shale oils as well as from various residual petroleum oil fractions derived from various sources. One such technique which has been suggested for recovering liquid hydrocarbons from tar sands and oil shale is called dense fluid extraction. The basic principals of dense fluid extraction at elevated temperatures are outlined in The Principals of Gas Extraction, by P. F. M. Paul and W. S. Wise, Mills and Boon Ltd., London, 1971. The dense liquid can be either a liquid or a dense gas having a liquid-like density. A number of prior art suggestions for recovering and upgrading hydrocarbons from oil shale and tar sands are discussed and summarized in U.S. Pat. Nos. 3,948,754 and 4,363,717 which are incorporated herein by reference.
Methods have been suggested for recovering liquid hydrocarbon fractions from various carbonaceous deposits with processes utilizing water. U.S. Pat. No. 3,051,644 discloses a process for the recovery of oil from oil shale which involves subjecting the oil shale particles dispersed in steam to treatment with steam at temperatures in the range of from about 370.degree. C. to about 485.degree. C., and at a pressure in the range of from about 1000 to 3000 psi. Oil from the oil shale is withdrawn in vapor form and admixed with steam. U.S. Pat. No. 3,796,650 describes a process for de-ashing and liquifying coal by contacting the coal with water, a reducing gas and a compound selected from the group consisting of ammonia and the carbonates and hydroxide of alkali metals at liquefaction temperatures. In U.S. Pat. No. 2,665,238, a process is described for recovering oil from oil shale which involves treating the shale with water in a large amount approaching the weight of the shale at a temperature in excess of 260.degree. C. and under a pressure in excess of 1000 psi. The amount of oil recovered increases generally as the temperature or pressure is increased.
The prior art also has suggested processes for cracking, desulfurizing, denitrifying, demetallating and generally upgrading hydrocarbon fractions by processes involving water. Examples of such prior art includes U.S. Pat. Nos. 3,453,206, 3,501,396, 3,586,621, 3,676,331 and 3,733,259. Many of the processes utilize various catalytic components such as metals deposited on a refractory inorganic oxide carrier, hydrogen, nickel spinel promoted with a barium salt of an organic acid in the presence of steam, carboxylic acid salts, etc.
U.S. Pat. No. 3,948,754 describes the process for recovering hydrocarbons from oil shale or tar sand solids and simultaneously for cracking, hydrogenating, desulfurizing, demetallating and denitifying the recovered hydrocarbons. The process comprises contacting the oil shale or tar sand solids with a water-containing fluid at a temperature in the range of from about 315.degree. to about 485.degree. C. in the absence of externally supplied hydrogen and in the presence of an externally supplied catalyst system containing a sulfur- and nitrogen-resistant promoter. Such catalyst can be selected from the group consisting of at least one soluble or insoluble transition metal compound, a transition metal deposited on a support, and combinations thereof. Preferably, the catalyst system additionally contains a promoter such as at least one basic metal hydroxide, basic metal carbonate, transition metal oxide, oxide-forming transition metal salts or combinations thereof.
U.S. Pat. No. 4,363,717 describes the process for the conversion of heavy hydrocarbon oils to motor fuel products. In particular, the heavy hydrocarbon oil is mixed with a metal halide catalyst and a solvent component under supercritical conditions to form (1) a dense-gas solvent phase which contains refined hydrocarbon crackate which is substantially free of metal halide catalyst content, and (2) a residual asphaltic phase. The phases are separated, and the dense-gas solvent extract phase is fractionated to remove the solvent and yield a refined hydrocarbon crackate fraction. The metal halides utilized are those metal chlorides, bromides and iodides which exhibit catalytic properties adapted for demetallation, desulfurization, denitrification and cracking of heavy hydrocarbon oil feedstocks under the process conditions. Examples of suitable metal catalysts include aluminum chloride, zinc chloride, gallium trichloride, cuprous chloride, cuprous bromide, etc.
The solvent which is present in the first step of the process described in U.S. Pat. No. 4,363,717 is indicated as being an important aspect of the invention. A solvent component preferably exhibits a dense-gas critical temperature limit in the range of between about 148.degree.-370.degree. C. Among the solvents indicated as being suitable, carbon dioxide, ammonia, water, methanol, ethane, hexane, benzene, dichlorodifluoro methane, nitrous oxide, diethylether, etc. are mentioned. Reference is made to U.S. Pat. No. 4,108,760 for its extensive disclosure of organic gases and liquids suitable for application as supercritical fluids in dense-gas extraction techniques.
A procedure for the extraction of oil from shale and tar sands by supercritical water preferably containing dissolved salts is described in DE No. 320719(A). Temperatures of from 360.degree.-600.degree. C. and pressures of 130-700 atmospheres are described as being used, and the water preferably contains one or more dissolved salts, especially, alkali, alkaline earth or ammonium chlorides or carbonates.